Primary and secondary cells have a loss of capacity on storing because of a self-discharge and dissolution of the metal electrodes. Thus, more specifically, the shelf life of a cell employing a zinc anode, such as a Leclanche system, is limited by, among other factors, the open circuit corrosion of the zinc anode which causes dissolution of the metallic zinc and discharge of hydrogen gas.
To avoid the corrosion of the zinc, a variety of corrosion inhibitors have been added to the electrolyte. One of the oldest and most effective corrosion inhibition techniques involves the amalgamation of the zinc by mercury. While a pre-amalgamation treatment of the zinc may be carried out, it is more conventional to apply mercuric chloride to the zinc as a component of the electrolyte.
Flat or planar batteries of the general type disclosed, for example, in U.S. Pat. Nos. 3,563,805; 3,617,387; 3,734,780; and the like, comprise superposed planar anode/cathode combinations possessing a separator disposed intermediate each anode and cathode and electrolyte disposed on or impregnated in the separator and in contact with respective facing surfaces of the anode and cathode.
Planar batteries of the type disclosed in the aforementioned U.S. patents are generally intended to be employed as an individual power source for portable electrically operated devices wherein the selected device design parameters are optimized by the availability and employment of a planar battery exhibiting reliability with respect to its power delivery characteristics. Batteries of the type in question presently are employed commercially to operate the various electrically powered systems of the photographic camera sold by Polaroid Corporation, Cambridge, Mass., U.S.A., under the trademark "SX-70". In such cameras, the battery, disposed as a component of a film pack for employment in and in combination with the camera, provides the electrical energy necessary to operate the camera's exposure control, film transport and photoflash systems and, accordingly, such battery is required to operate in a sequential series of power generating modes which may or may not be interrupted by more or less extended recovery and/or storage times and under which conditions to deliver the required series of high current pulses dictated by the photographic system design.
Particular problems of amalgamation are presented with the above-described flat, planar batteries. Generally, powdered zinc is employed as the anode, which contains a relatively large amount, e.g., 5% or more, of zinc oxide and which presents a large surface area to the electrolyte. Amalgamation proceeds rapidly with the available zinc surfaces being protected by the interaction of the zinc with mercuric ions to form a zinc amalgam.
Subsequent to amalgamation and in contact with the electrolyte, the zinc oxide portion of the anode slowly dissolves providing fresh, unamalgamated zinc surfaces which result in increased hydrogen gas generation and attendant increase in impedence and general deterioration of the battery. Also, if less than full surface coverage by electrolyte occurs initially upon assembly subsequent redistribution of mercury-ion depleted electrolyte will also result in inadequately amalgamated zinc surfaces. The art has recognized that the effectiveness of amalgamation to inhibit corrosion is superior at room temperature but inadequate at elevated temperatures.
Copending application Ser. No. 50,354 filed June 26, 1970 now U.S. Pat. No. 3,945,849 is directed to the employment of quaternary ammonium halide as a corrosion inhibitor for zinc anodes. This inhibitor has been found to be more effective at elevated temperatures than at room temperature.
A novel corrosion inhibition system has now been found which is not susceptible to the deficiencies of the prior art.